The present invention relates to a solid-state imaging apparatus and a manufacturing method thereof, and more particularly to a small-sized solid-state imaging apparatus including a solid-state image pickup element, such as a surveillance camera, a medical camera, or a vehicle camera, and a manufacturing method thereof.
An imaging apparatus of this kind receives an image through an optical system such as a lens, and outputs the image in the form of an electric signal. Recently, in accordance with miniaturization and enhancement of the performance of such an imaging apparatus, also the size of a camera is reduced, and an imaging apparatus is used in various fields and expands its market as an image inputting device.
In a conventional imaging apparatus using a solid-state image pickup element, each of components such as a lens, the solid-state image pickup element, and an LSI on which a driving circuit for the element and a signal processing circuit are mounted, has a shape of a case or a structure member, and the components are combined with each other. Conventionally, a mounting structure based on such a combination is formed by mounting elements onto a flat printed circuit board.
In order to further miniaturize such a device, a three-dimensional printed circuit board 101 shown in FIG. 7 was proposed in Japanese Patent Publication No 2001-245186. The printed circuit board 101 is made of a resin in which a mounting member is configured by a leg portion 101A having a rectangular table-like shape, and a body portion 101B formed on the leg portion, and a through-opening portion 101C is formed in the interface between the leg portion 101A and the body portion 101B. A printed wiring pattern 105 is formed on the three-dimensional printed circuit board on side of the rear face of the leg portion 101A. A lens is fitted into the inner periphery of the body portion 101B. While being centered at the optical axis 117 of the lens, an optical filter 103 is placed above the through-opening portion 101C, and a solid-state image pickup element 104 and chip components 108 are placed below the through-opening portion. As shown in a section view of FIG. 8, the printed circuit board is connected by using solder 114 through the printed wiring pattern 105 formed on the leg portion 101A, to a main board 113 of an apparatus such as a portable telephone or a personal computer. FIG. 9 is a view showing main portions of the connections. The solid-state image pickup element 104 is connected to the printed wiring pattern 105 formed on the leg portion 101A, through bumps 106 formed on the surface of the image pickup element 104, and then sealed by a sealing resin 107 to accomplish the connections with the three-dimensional printed circuit board 101.
The identical portions are denoted by the identical reference numerals.
In the mounting process, as shown in FIGS. 10A to 10C, a method is employed in which, after the three-dimensional printed circuitboard 101 is molded (FIG. 10A), the solid-state image pickup element 104 is attached to the board (FIG. 10B), and the optical filter 103 is then attached (FIG. 10C).
In a heating step in the process of mounting the solid-state image pickup element 104 onto the three-dimensional printed circuit board 101, the three-dimensional printed circuit board 101 is largely deformed, and a very high stress is generated in connecting portions between the solid-state image pickup element 104 and the three-dimensional printed circuit board 101, so that a connection failure due to cracking often occurs.
Usually, such a three-dimensional printed circuit board is obtained by injection molding, However, there is a problem in that fillers, which are often used in order to reduce the coefficient of expansion of a resin material, cannot be added in an amount larger than a given one from the viewpoints of the molding accuracy and the durability of molding dies.
A thermoplastic, resin usually used in injection molding has a straight-chain molecular structure, and hence exhibits anisotropic properties that the coefficient of linear expansion is small, in the molecular bonding direction and large in a direction perpendicular to the bonding direction. In such a resin, fillers are oriented in the molding flow direction to exhibit, further anisotropic properties that the coefficient is large in a direction perpendicular to the molding flow direction.
In a heating step in the process of mounting a solid-state image pickup element onto a three-dimensional printed circuit board, the three-dimensional printed circuit board is largely deformed, and a very high stress is generated in connecting portions between the solid-state image pickup element and the three-dimensional printed circuit board, so that a connection failure due to cracking often occurs.
Usually, such connecting portions between a solid-state image pickup element and a three-dimensional printed circuit board are configured by pads disposed on the solid-state image pickup element, and terminals of the three-dimensional printed circuit board. The connection between them is realized by connection using an electrically conductive adhesive agent such as silver paste, ultrasonic bonding, thermocompression bonding, or the like.
In any of the methods, the adhesion of the solid-state image pickup element is easily broken because of thermal deformation of the three-dimensional printed circuit board, and this causes the production yield to be lowered.
When a printed circuit board is three-dimensionally structured, miniaturization is enabled, but thermal distortion is larger than that in the case of a usual two-dimensional structure, thereby causing a large problem in that deformation due to the difference in coefficient of expansion blocks improvement of the yield.
Usually, the optical filter 103 is made of a quartz refraction plate, or a glass material such as IR (infrared) cut-off coated glass, and is lower in coefficient of thermal expansion and also in thermal deformation than a resin material.
Therefore, it may be contemplated that, when the optical filter 103 is previously attached, thermal deformation during the process of attaching the solid-state image-pickup element is largely improved Actually, however, the process of attaching the solid-state image pickup element must be conducted so that direct bonding is first done through bumps and the vicinity of connecting portions is then sealed by a sealing resin. Consequently, there arise problems in that a gas generated during the sealing step is trapped in the through-opening portion 1C to react with the surface of the solid-state image pickup element as a result of application of heat, and that the generation of the gas rises the internal pressure to deteriorate the solid-state image pickup element or deform the three-dimensional printed circuit board.
For the foregoing reasons, in a conventional structure, a method is employed in which an optical filter is attached after a solid-state image pickup element is attached.
Therefore, the production requires a large number of steps. Also the positioning operation in each attaching step is one of the causes of blocking the improvement of the productivity.